Thoracentesis is an invasive procedure to remove fluid or air from the pleural space for either diagnostic or therapeutic purposes; a cannula, hollow needle or catheter, is introduced into the chest and pleural fluid is aspirated through it.
With regard to the diagnostic purposes, pleural fluid can provide information enhancing the practitioner's understanding of the underlying pleural pathophysiology when an effusion is present, thereby allowing the source and/or cause of the pleural effusion to be found—common causes include cancer, congestive heart failure, pneumonia and tuberculosis, as well as recent surgery.
With regard to the therapeutic purposes, thoracentesis can be useful when a large volume of fluid is present; such removal will tend to improve patient comfort and lung function. Second, the measurement of pleural pressure also helps to differentiate between lung entrapment and trapped lung, and as such allows for the safer removal of large effusions. Third, it is a useful tool to select appropriate patients with malignant pleural effusions for pleurodesis.
Pleural manometry during large-volume procedures allows the practitioner to monitor changes of pressure during those procedures and thus to avoid pleural pressures (i.e. below below −20 cm H2O) which are excessively negative—pressures which might otherwise lead to the onset of re-expansion pulmonary edema. In addition, measurement of lung elastance by way of pressure has been proven to be a predictor of successful pleurodesis.
In Pleural manometry: Technique and Clinical Implications, Doelken et al (Chest 2004; 126; 1764-1769), two widely used means of pleural manometry—namely a vertical-column water manometer with an interposed resistive element, and a haemodynamic transducer connected to a standard physiologic system—are discussed, along with the disadvantages of both. The paper goes on to present a system of pleural manometry comprising a flexible thoracentesis catheter and a water manometer consisting of two lengths of IV tubing connected through a 22 gauge needle inserted into an injection terminal. This system is connected to the zeroing port of a pressure transducer and, once both are purged of air, and the electronic system is zeroed at the level the thoracentesis catheter is introduced into the patient, measurements can be performed initially and after each 250 ml of fluid is withdrawn.
Disadvantageously, this is not a real-time system and as such the dynamic measuring of lung pressure cannot be undertaken. In any context, but particularly in an emergency context, where lung pressure is likely to change swiftly, such start-stop measurement is sub-optimal, as well as being an unwieldy and therefore impracticable procedure.
The closest known prior art consists of the “Compass” thoracentesis device by Mirador medical. The Mirador device requires the movement of the fluid through the manometer, along a tube, and through a first one-way valve to a reservoir such as a syringe barrel. The user must then pause after aspiration of a first quantity of fluid to take a measurement from the manometer, before ejecting the fluid through a second one way valve. After this, aspiration can be done in real time.
Because the fluid must travel through the manometer, the Compass manometer itself will be thrown away after a single use.
Further, prior to the aspiration of the first quantity of fluid, the manometer cannot be used to measure the pleural fluid pressure. Instead, during this period, a large negative pressure is observed; this is not the patient's pleural pressure, this is the pressure being generated by the drainage system.
Further, the assembly of apparatus comprises several parts which must be assembled before the procedure takes place, and this can be unwieldy.
The prior art devices share the disadvantage that they all take rather a long time to use—in particular, they all require a calibration step to be undertaken, which is time consuming and requires a certain amount of prior knowledge in order to be effected. It is possible to envisage a situation in which the user does not know how to prime a prior art manometer and as such produces data which is inaccurate, leading to mistreatment of the patient.
Current practice has been that after insertion of the catheter in to the pleural space the operator would have to prime the catheter and allow fluid to be placed over the transducer. The manometer of the invention allows for measurement directly after insertion.
It is amongst the aims of the invention to attempt solutions to these and other problems.